1. Field of the Invention
The present invention relates to switching power supplies, and more specifically, to switching power supplies, which are primarily designed to be energized from the AC mains supply and are provided with a back-up DC voltage supply to provide transient-free DC output power during brown-out or failure of the AC mains supply.
2. Discussion of the Relevant Art
There are many circuit arrangements available for converting DC power into AC output voltage and conversely changing AC input voltage to DC output voltage that include various types of DC output regulation. With the advent of computers, and their sensitivity to input line voltage (AC mains) variations and transients appearing thereon, it has become necessary to provide a regulated DC power source for operation of these computers that is not subject to temporary AC mains failures or intermittent brown-out conditions. These conditions, including transients or voltage spikes such as those caused by turning on equipment which draw heavy amounts of power from the AC power lines, and those that are generated during operation or upon shut-down of equipment can create havoc if they were permitted to reach the output voltage powering today' computers. Consequently, some computer designs incorporate a sensing logic bus which is continually monitored by the computer logic circuitry. If the input line voltage were subjected to a sudden loss of voltage (transient), the logic circuitry senses this change and provides a signal voltage that freezes the computer memories or provides for their orderly shut-down, preventing a complete erasure of all the data stored therein and thus permit the computer to continue its operation as soon as the input voltage returns to its normal range of operation.
There are numerous techniques in use today which provide different protective measures for computer memories so that a complete reprogramming is not necessary the information previously stored in the memories remains intact.